Wilfredo, that's very impressive! You haven't seen these because they were made by the artists who sent them. They would be called Cinderellas in the philately world, in mail-art we call them artistamps. We make up ficticious postal authorities, countries, etc. and send them to each other and to other people. For more information you can visit http://www.theolatheposte.com/http://www.art.net/kiyoteihttp://artistamp.org/